Throttle valve control mechanism for internal-combustion engines



Oct. 24, 1944. A A |SS|GQN|5 2,361,103

THROTTLE VALVE CONTROL MECHANISM FOR INTERNAL-COMBUSTION ENGINES Filed Sept. 27, 1943 I llillll' l i I I #A Patented Oct. 24, 1944 THROTTLE VALVE CONTROL MECHANISM FOR INTERNAL-COMBUSTION ENGINES Alexander Arnold Issigonis, Cowley, Oxford, England, assignor to Morris Motors Limited, Cowley, Oxford, England Application September 27, 1943, Serial No. 504,014

In Great Britain October 2A), 1942 2 Claims.

This invention relates to the throttle valve control mechanisms used for controlling the supply of combustible mixture to the cylinders of vehicle and other internal combustion engines.

It is a, common practice to provide such a mechanism with an adjustable stop for determining the extent to which the valve can be moved towards its closed position, this stop being usually so adjusted as to prevent complete closing of the valve and to allow (when the engine is idling) suficient flow past the valve to keep the engine in motion. On some engines and more particularly two-stroke engines when the valve is allowed to move quickly from the fully open position to the nearly closed position determined by the stop, there results a considerable depression of pressure in the induction system leading to the engine, with a consequent risk of the combustible mixture in the said system becoming ignited. This condition is undesirable and may sometimes be dangerous. The object of the present invention is to provide an improved throttle valve controlling mechanism whereby the said risk is obviated.

The accompanying drawing illustrates one mode of carrying the invention into effect.

In the drawing, the general outline of a carburetter is indicated by the letter a, the air inlet being at b and the mixture outlet at c. The outlet is adapted to be connected to the induction system of the engine. The carburetter shown in the drawing is of the down draught type. In the outlet is pivoted the throttle valve d, this being of the usual butterfly type. To the spindle e of the valve is secured a bell crank lever f, the long arm of which is connected by a link g to a pedal h, the latter being actuated in the direction for closing the valve by a spring i. The short arm of the lever is provided with an adjustable screw i which can abut the stop Ic.

According to the form of my invention illustrated by the drawing the stop Ic is slidably supported in a casing l which also carries a plunger m slidable in a direction at right angles to-the stop, and the lower end of the plunger m is tapered as shown. The upper end of the plunger m is attached to a diaphragm n contained in a chamber o formed by the casing, the diaphragm being gripped in agas tight manner around its peripheral portion between two parts of the casing. The upper part of the casing contains a spring p which tends to urge the diaphragm and plunger in the downward direction, and this end of the casing is connected by a pipe q to a point on the outlet c at the engine side of valve d.

Normally the diaphragm occupies a central position in the chambero and when the diaphragm is in this position the plunger occupies a position in which its cylindrical surface is in contact with the adjacent end of the stop. This condition determines the partially closed position of the valve d as indicated by the dotted lines in the drawing, this being the position occupied by the valve during normal slow running or idling of the engine. Adjustment of this position of the valve can be eiected by the screw i. The plunger is held in the said lower position by the spring p which is suiciently strong to overcome the upward thrust caused by the pressure of the stop on the tapered portion of the plunger.

When a suicient depression of pressure occurs in the induction system the atmospheric pressure acting on the underside of the diaphragm moves the latter upwards against the action of the spring p into the position shown, thereby raising the plunger and bringing the tapered surface of the plunger behind the stop. The stop can now move to the position in which it allows the valve to be fully closed as represented by the full lines in the drawing.

When the engine is running under normal speed and load conditions the diaphragm occupies its central position and the tapered portion of the plunger lies below the stop. Consequently the latter is held in the position corresponding to partial closing of the valve. So long as the pressure in the induction system continues to be insuicient to affect the diaphragm, the stop remains in the position mentioned. But if the throttle is allowed to close rapidly and if in consequence a suicient depression of pressure is set up in the induction system, the plunger is raised to the upper position shown by the drawing, allowing the stop to take up its other position and permit the throttle valve to become fully closed. Complete closure of the throttle valve prevents continued entry of mixture to the engine with the result that the engine speed falls rapidly and the pressure in the induction system consequently rises. Thereupon the diaphragm and plunger return to the normal position causing the stop to be pushed to the other of its two positions and the valve to open suiciently to maintain the engine in motion. A

By interrupting the supply of mixture tothe engine temporarily when the throttle valve is allowed to close rapidly the condition which otherwise tends to result in a risk of ignition of the charge in the induction system is obviated.

As already stated the invention is more especially useful on two-stroke engines but it may be applied if desired to other internal combustion engines, as used on vehicles or 'for other like` purposes.

The invention is not, however, restricted to the example described as subordinate constructions! details may be varied to suit different requirements. Thus the diaphragm may be replaced by a piston slidablejn a cylindrical chamber, and

instead of a slidable stop an angularly movable stop may be used.

Having thus described my invention what I movement of the throttle valve. a relatively movable abutment by which the stop is constantly supported,and means responsive to the pressure in the portion of the induction system between the valve and ensine for varying the position oi the abutment, the latter being shaped and arranged so that it is movable by the said means between a normal position i'n which the stop can serve to prevent complete closure of the valve. and another position in which the stop permits complete closure of the valve.

2. A throttle valve control mechanism as claimed in claim 1, in which the abutment consists of a slidable plunger having a tapered portion which permits movement of the stop into the position for permitting complete closure of the valve.

ALEXANDER ARNOLD ISSIGONIS. 

